00. Preface

A vacuum interrupter, also known as a vacuum switch tube, plays a crucial role in power systems as the core component of vacuum circuit breakers. Its primary function is to utilize the superior insulating properties of vacuum within the tube to rapidly extinguish arcs and suppress current after cutting off power in medium- and high-voltage circuits. This prevents accidents and unexpected incidents. Vacuum interrupters are widely used in power transmission and distribution control systems, as well as in fields such as metallurgy, mining, petroleum, chemical engineering, railways, broadcasting, telecommunications, and industrial high-frequency heating distribution systems. They offer advantages such as energy and material savings, fire and explosion resistance, compact size, long service life, low maintenance costs, reliable operation, and environmental friendliness.
Vacuum interrupters can be categorized by use into circuit breaker interrupters and load switch interrupters, where the former is mainly applied in substations and power grid facilities, and the latter serves end users of the power grid.

01. Basic Knowledge of Vacuum Interrupters

1.What is Vacuum?
Vacuum refers to a gas state with pressure significantly lower than atmospheric pressure within a given space. The degree of gas rarity in a vacuum is typically expressed by its vacuum level, measured in pressure values. Higher pressure indicates lower vacuum levels, and vice versa. In vacuum interrupters, the vacuum level is generally between 10^-3Pa～10^-4Pa.

2.What is a Vacuum Interrupter?

A vacuum interrupter, also called a vacuum switch tube or vacuum bubble, is the critical component of a vacuum circuit breaker. It consists of a pair of electrodes (contacts) and other parts sealed in a vacuum. By leveraging the excellent insulating and arc-extinguishing properties of vacuum, it enables the circuit to open or close and extinguishes arcs promptly after cutting off power, suppressing current flow effectively.

3.Types of Vacuum Interrupters

By Shell Material: Glass vacuum interrupters, ceramic vacuum interrupters.

By Application:

• Circuit breaker vacuum interrupters

• Load switch vacuum interrupters

• Contactor vacuum interrupters

• Recloser vacuum interrupters

• Sectionalizer vacuum interrupters

• Other specialized vacuum interrupters

02. Basic Structure of Vacuum Interrupters

The primary components of a vacuum interrupter include the airtight insulation system, conductive system, shielding system, and contact system.

1.Airtight Insulation System

Comprised of an airtight insulating shell (glass or ceramic), a movable end plate, a fixed end plate, and a stainless steel bellows.

Insulating Shell:

Materials: Glass, ceramic, and microcrystalline glass.

• Microcrystalline glass, being costly, is rarely used.

• Glass, with weaker structural strength, is being phased out.

• Ceramic, with superior comprehensive performance, is most widely used.

Function: Provides insulating support and forms part of the airtight insulation system.

Bellows:

Materials: Made from stainless steel with a thickness of 0.1–0.2 mm.

Function: Enables movement of the movable electrode within a specific range and maintains a high vacuum seal. Bellows must have excellent mechanical durability.

2.Conductive System

Composed of fixed conductive rods, fixed arc-running surfaces, fixed contacts, movable contacts, movable arc-running surfaces, and movable conductive rods.

The conductive system is divided into the fixed electrode (fixed conductive rod, fixed arc-running surface, fixed contact) and the movable electrode (movable conductive rod, movable arc-running surface, movable contact).

The operation mechanism moves the movable conductive rod, causing the contacts to close and complete the circuit. When breaking the current, the contacts separate, forming an arc that extinguishes at current zero, completing the circuit disconnection.

3.Shielding System
The shielding system comprises a shielding cylinder, shielding cover, and other components.

Shielding Cylinder:

Materials: Made from oxygen-free copper, stainless steel, electrical pure iron, or copper-chromium alloy.

Functions:

Reduces pollution on the inner wall of the insulating shell caused by metal vapor and droplets during arcing, preventing insulation degradation or flashovers.

Improves the electric field distribution within the vacuum interrupter, aiding in miniaturization, especially for high-voltage applications.

Condenses arc-generated products, absorbing a large portion of the thermal energy and enhancing breaking capability.

4.Contact System

Contact Design:

Generates transverse or longitudinal magnetic fields to control arc distribution and enhance breaking performance.

Common structures include cylindrical contacts, transverse magnetic field contacts (e.g., spiral groove), and longitudinal magnetic field contacts (e.g., slanted grooves).

Contact Materials:

Commonly used materials include copper-bismuth alloy, copper-chromium alloy, and copper-tungsten alloy, with copper-chromium alloy being the most prevalent.

03. Magnetic Field Types and Arc Extinction

1.Transverse Magnetic Field Contacts:
Generates a magnetic field perpendicular to the electrode axis. This field enables rapid arc movement along the contact surface, preventing severe melting and aiding in fast insulation recovery after current zero.

2.Longitudinal Magnetic Field Contacts:
Produces a magnetic field aligned with the electrode axis. This field helps evenly distribute arc spots on the contact surface, reducing localized melting and enhancing breaking capacity.

Large-capacity vacuum interrupters predominantly use longitudinal magnetic field contacts due to their advantages of reduced electrical wear, longer lifespan, and superior breaking performance.